I am making wine jelly and have run out of lemons. I have some citric acid in the pantry. Can I use the citric acid instead? The jelly calls for half a cup of lemon juice. If I can use it, how much citric acid would I use?
Yes, you can. In fact, many canning and jarring recipes specifically call for citric acid.
Presumably you are using citric acid in its dried, crystalline form. In that case, a solution of around 4% citric acid (e.g. 4gm in 100ml of water) should be around the same strength as lemon juice.
This link http://www.livestrong.com/article/520416-how-to-substitute-lemon-juice-for-citric-acid/ says 1/4 teaspoon of citric acid substitutes 1 tablespoon of lemon juice.
So for half a cup of lemon juice, use two teaspoons of citric acid, and compensate for the missing liquid.
I googled it, and it says 1/4 teaspoon citric acid= 1tablespoon lemon juice 1 teaspoon citric acid =1/4 cup lemon juice
I just read you can add 3g citric acid/l or kg to make jam or marmalade.